[mapserver-dev] PostGIS "curvepolygon" support

[Astrid Emde]

Frank Warmerdam schrieb:
> Astrid Emde wrote:
>>>  Curiously could this mean adding to the PostGIS driver a means of
>>>  going from curve to shapeObj? As opposed to adding a curve shape
>>>  type within MapServer.
>>
>> Could you please discuss a possible solution and estimate the costs? 
>> Who would be the contact person concerning this enhancement?
>>
>> Maybe there are other MapServer users interested in this enhancement 
>> and would also sponsor the implementation.
>
> Astrid,
>
> If a solution where the curves are converted to an approximating 
> linestring
> while being converted from wkb to shapeObj is acceptable it could be done
> easily inside the force_to_lines() and force_to_polygons() functions in
> mappostgis.c.  I have done this in OGR for many datasources with 
> curves and
> could incorporate the same capability in MapServer's postgis driver quite
> easily (ie. a couple hours).  I would be willing to do this gratis on
> account of the WhereGroup's past support for MapServer, GDAL/OGR and 
> OSGeo
> as long as you folks can do final testing.
>
> Of course the ideal is to add arcs as a first class geometry type in
> MapServer for more efficient and precise handling but that is a 
> substantially
> bigger job.
>
> Best regards,
Hi Frank,

thanks for your answer and the nice offer. There would be a budget for 
this enhancement so you could get a payment for the implementation. 
Still I would do the testing and give feedback.

The main thing would be to get a sustainable solution with good 
performance which bringsforward the mapServer project as maybe more and 
more user will need this functionality.

We have mixed data (linestrings mixed with compoundcurves and 
circularstring and on the other hand polygons mixed with CURVEPOLYGONs) 
in one feature table. At the moment we create a second geometry column 
where we create with st_curvetoline(the_geom)  linestrings from our 
curves. We used this function in the mapfile itself but the performance 
was too bad to do the processing on every request.

It would be good to define a MapServer LAYER from type LINESTRING or 
POLYGON and display linestrings/compoundcurves/circularstring and 
polygons/CURVEPOLYGONs.

Now about the "bigger job" to add arcs as a first class geometry type in 
MapServer:
* what advantages would this bring?
* could we be able to handle both geometry types 
linestrings/compoundcurves/circularstring and polygons/CURVEPOLYGONs 
within one LAYER
* what about the performance

What do you think?

-- 


Astrid

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 Astrid Emde
 WhereGroup GmbH & Co.KG
 Siemensstraße 8
 53121 Bonn
 Germany

 Fon: +49(0)228 90 90 38 - 19
 Fax: +49(0)228 90 90 38 - 11

 astrid.emde at wheregroup.com
 www.wheregroup.com

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